Hard facing of metal substrates

ABSTRACT

Method for hard-facing metal substrates is disclosed using a hard facing material consisting essentially of combined vanadium, tungsten and carbon and from about 5 to about 40% by weight of chromium carbide with up to 15% by weight in the aggregate of cobalt, iron, molybdenum and nickel.

The present invention relates to the hard facing of iron base alloysubstrates. More particularly, the present invention relates to the hardfacing of iron based alloy substrates using as the hard-facing materiala vanadium, tungsten, chromium and carbon containing composition toprovide improved wear and impact resistance.

Hard facing of substrates, e.g. metal surfaces*, is a common industrialpractice, for example, cast particulate tungsten carbide (W₂ C--WC) orcobalt bonded WC, usually encased in a steel tube, is deposited by hardfacing techniques or iron base alloys in making wear resistant cutters,earth moving equipment and the like. It has been found, however, thatdue possibly to the inherently different physical properties of basemetal and tungsten carbide, the hard facing material has a tendency tobecome unevenly distributed in the molten portion of the metal substrateand as a result, undesired variations in hardness can occur in theresulting solidified hard-faced surfaces.

Also, during the deposition of both cast and cobalt-bonded tungstencarbide on iron and steel substrates, the molten iron in the substratedissolves some of the tungsten carbide and upon cooling results in theprecipitation of the mixed carbides (FeW)₆ C and Fe₃ W₃ C according tothe formula 3WC+9Fe→Fe₃ W₃ C+2Fe₃ C, thus resulting in substantialdepletion of the deposited tungsten into less wear resistant phase.

In instances where tungsten carbide is employed in hard facing, due tothe high density of tungsten carbide, a relatively large weight oftungsten carbide is required for adequate hard facing.

It is accordingly an object of the present invention to provide ahard-facing method using a material containing vanadium and chromiumcarbide in combination with tungsten and carbon to produce a hard-facedsurface having wear resistant properties at least comparable to thoseprovided by the use of conventional tungsten carbide.

Other objects will be apparent from the following description and claimstaken in conjunction with the drawing which shows a graph of test dataobtained in accordance with the practice of the present invention.

The FIGURE of the drawing shows graphically wear and abrasion results ofhard facing deposits obtained using chromium carbide containing hardfacing material in accordance with the present invention; the FIGUREalso shows wear and abrasion results for hard facing material notcontaining chromium carbide.

The present invention is directed to an improvement in conventionalmethods of hard-facing substrates which comprises employing as the hardfacing material a solid material consisting essentially of chemicallycombined vanadium, tungsten, and carbon in weight proportions of 0.75VC, 0.25 WC and from about 5 to about 40% by weight of chromium carbidein proportions of Cr₃ C₂, from 0 to 100% of said chromium carbide beingchemically combined with said 0.75 VC, 0.25 WC in the form of avanadium, tungsten, chromium carbide having the empirical formula:

    [A Cr.sub.1.5.B0.75 V, 0.25 W]C

where A=0.05 to 0.4

B=0.6 to 0.95

A+b=1.0

the aforedescribed composition can also contain up to 15% by weight inthe aggregate of cobalt, iron, nickel and molybdenum, preferably 3 to 6%cobalt.

While various techniques can be used for producing the above describedhard facing material from conventional starting materials, includingelemental vanadium, tungsten, chromium and carbon, the preferred form ofthe hard facing material for use in the method of the present inventionis a particulated cold pressed and sintered, e.g. under hydrogenatmosphere or vacuum, and subsequently granulated material illustratedby example in the present specification. In these examples, the startingvanadium, tungsten, chromium and carbon materials are blended, compactedand sintered under a hydrogen atmosphere at elevated temperatures, e.g.about 1200°-1600° C. and for periods, e.g. 1/2 to 3 hours, sufficient toproduce material as aforedescribed.

A particular embodiment of the present invention comprises a hard facingrod in conventional form for use in hard facing iron and iron base alloymetal substrates, e.g. mild steel, Hadfield steels and the like. Such ahard facing rod comprises a metallic sheath or tube formed of the usualmetals for such purposes such as iron, steel, aluminum, copper and thelike containing therein a hard facing composition as previouslydescribed.

The hard facing method of the present invention can be used with knowngas and electric welding techniques, e.g. gas welding, arc welding andother practices described in the "Master Chart of WeldingProcesses"--American Welding Society (1969), using conventional fluxes.

The hard facing method of the present invention can also be used withknown plasma flame spraying or coating techniques ("Flame SprayHandbook" Volume III--METCO INC. (1965).

In the hard facing of metal substrates in accordance with the presentinvention by the above-noted conventional techniques the metal substrateand the applied hard facing material become metallurgically bonded.

The following examples illustrate materials for use as hard-facingcompositions in accordance with the present invention.

EXAMPLE I

The following materials were used to obtain a cold pressed, sinteredhard-facing composition containing 90% by weight of 0.75 VC, 0.25 WCC+3%Co material and 10% by weight of Cr₃ C₂ for use in the presentinvention:

(a) 3111.8 g of a commercially available material (Union CarbideCorporation) containing mixed V₂ C+VC, sized 65 mesh and finer havingthe following analysis:

84.69% V

13.20% c

1.10% o

balance moisture and incidental impurities.

(b) 244.5 Acheson* brand G39 graphite powder, sized 200 mesh and finer.

(c) 135 g cobalt powder, extra fine grade from African Metals Corp.

(d) 1024.3 g of UCAR* tungsten metal powder (2 micron).

(e) 500 g of chromium carbide (Cr₃ C₂) sized 325 mesh and finer. The Cr₃C₂ had the following analysis:

86.67% Cr

12.60% C

0.04% o

0.29% fe

The powders were placed in a one cubic foot ball mill with 75 lbs. of1/2-in. dia. balls and turned at 57 RPM for 18 hours. After 18 hoursmilling, the material was pressed into pellets in a 2 inch diameter dieat a fifty ton load. The pellets were crushed into granules. Thegranules were placed in graphite boats and sintered in a pure hydrogenpush-through molybdenum-wound heat-treating furnace. The sintering cyclewas as follows: The graphite boat was placed inside the furnace door for1/2 hour, to diffuse out residual atmospheric gases. The boat then wasadvanced to a 900°-1200° C. zone to allow the reduction of any residualoxides and the removal of the reduction products. The the boat wasadvanced into the hot zone at 1500° C. for 11/2 hr. to provide sinteringof the cold pressed material. The boat was then pushed out of the hotzone into a water-cooled chamber and brought to room temperature inabout 15 minutes. The granules were lightly bonded together but wereeasily separated in a jaw crusher. Aside from the contained cobalt andCr₃ C₂ the material was formed of chemically combined vanadium, tungstenand carbon, 0.75VC, 0.25WC and had the following analysis by weight:

V 51.19%

w 20.80%

cr 8.46%

Fe 1.60%

Co 3.75%

C 13.58%

d 0.34%

n 0.14%

the cold pressed and sintered material was prepared in the foregoingexample and using various amounts of Cr₃ C₂, was employed as a hardfacing material in the following manner.

For electric welding deposits 10×30 mesh granules were packed into 12in. long 0.250 in. O.D., 0.190 in. I.D. mild steel tubing. The granulescomprised about 45% by weight of the rod. The rod was fluxed forelectric deposition and deposited on an iron substrate at 180 ampD.C.R.P.; for gas welding deposits 65×150 mesh granules were similarlypacked into mild steel tubing and fluxed for oxyacetylene welding anddeposited by oxyacetylene techniques with a minimum of penetration on amild steel substrate with a carburizing flame.

The resulting hard-faced surfaces were tested for abrasion resistanceusing a rubber wheel-sand wear and abrasion test. The wear and abrasiontest was as follows: A 1 inch×3 inch×1/2 inch thick steel substrate ishard faced by depositing a hard faced material thereon and the hardfaced surface is ground flat. A 91/8 inch O.D. by 1/2 inch wide neoprenecircular disk (durometry hardness shore A 50-60) is used with the hardfaced surface being loaded with 38 ft.-lbs. of force against theneoprene disk. Silica sand (sand blast sand size 2, QROK) is fed inexcess between the neoprene disk and the hard faced surface with theneoprene disk being turned at 200 RPM for 200 revolutions. The specimenunder test is weighed before and after and the procedure is repeateduntil a constant weight loss is obtained for repeated tests and thisweight loss is used as a measure of wear and abrasion resistance. Theresults obtained are shown in the graph of the drawing and compared withthe results obtained without chromium carbide additions. In thedrawings, A and B are the results obtained using a sintered mixture of0.75VC, 0.25WC+3Co and Cr₃ C₂ ; A' and B' are the results obtained usinga mechanical mixture of 0.75VC, 0.25WC+3Co with chromium carbide, Cr₃C₂.

EXAMPLE II

The following materials were used to obtain a cold pressed, sinteredhard-facing composition containing 70% by weight of 0.75VC, 0.25WC+3%Comaterial and 30% by weight of chromium carbide in proportions of Cr₃ C₂for use in the present invention:

(a) 2588.4 g of a commercially available material (Union CarbideCorporation) containing mixed V₂ C+VC, sized 65 mesh and finer havingthe following analysis:

(b) 428.5 g Acheson* brand G39 graphite powder, sized 200 mesh andfiner.

(c) 150 g cobalt powder, extra fine grade from African Metals Corp.

(d) 821.4 g of UCAR* tungsten metal powder (2 micron).

(e) 1306.7 g of Elchrome* metal powder sized 100 mesh and finer.

The powders were placed in a one cubic foot ball mill with 75 lbs. of1/2-in. dia. balls and turned at 57 RPM for 18 hours. After 18 hoursmilling, the material was pressed into pellets in a 2 inch diameter dieat a fifty ton load. The pellets were crushed into granules. Thegranules were placed in graphite boats and sintered in a pure hydrogenpush-through molybdenum-wound heat-treating furnace. The sintering cyclewas as follows: The graphite boat was placed inside the furnace door for1/2 hour, to diffuse out residual atmospheric gases. The boat then wasadvanced to a 900°-1200° C. zone to allow the reduction of any residualoxides and the removal of the reduction products. The boat was advancedinto the hot zone at 1500° C. for 11/2 hr. to provide sintering of thecold pressed material. The boat was then pushed out of the hot zone intoa water-cooled chamber and brought to room temperature in about 15minutes. The granules were lightly bonded together but were easilyseparated in a jaw crusher. Aside from the contained cobalt the materialwas formed of chemically combined chromium, vanadium, tungsten andcarbon in accordance with the present invention and had the followinganalysis:

V--40.20%

w--15.15%

cr--24.06%

T.c.--13.03%

co--4.80%

O--0.02%

n--0.10%

fe--3.24%

The wear rate of the deposits for material in accordance with thepresent invention is at least as good as that of cast tungsten carbideand superior to the vanadium, tungsten carbide material tested which didnot contain chromium carbide.

A further advantage is the high toughness of the deposit provided by thematerial in accordance with the present invention.

What is claimed is:
 1. A hard-facing rod comprising a metal sheathhaving a core of hard facing material consisting essentially ofchemically combined vanadium, tungsten and carbon in weight proportionsof 0.75VC, 0.25WC and about 5% to 40% by weight of Cr₃ C₂ admixedtherewith from 0 to 100% of said Cr₃ C₂ being chemically combined withsaid chemically combined vanadium, tungsten and carbon in the form of avanadium, tungsten, chromium carbide having the empirical formula:

    [ACr.sub.1.5.B0.75V,0.25W]C

where A=0.05 to 0.4 B=0.6 to 0.95 A+b=1.0and up to 15% by weight in theaggregate of cobalt, iron, molybdenum and nickel.
 2. A hard-facing rodin accordance with claim 1 wherein said hard-facing composition is inthe form of a sintered solid material in particulated form.